Degeneration of intervertebral discs (IVD) is associated with low back pain and is a serious public health problem in the US, affecting more that 25% of adults (Deyo et al., 2006). Current therapies for treatment of pain resulting from IVD degeneration include spinal fusion, discectomy, and total disc replacement. Each of these techniques, however, has limitations. Fusion and rigid fixation limits mobility and may lead to degeneration of discs in the adjacent motion segments, while discectomy results in loss of disc height and alters the biomechanics of the spine (Lee, 1988; Schlegel et al., 1996). These methods, on the whole, do not repair the degenerated disc or restore its original function. As a result, there has been recent increasing interest in preserving as much of the disc tissue as possible and in developing new techniques to truly repair damaged discs. Specifically, strategies to replace and regenerate the nucleus pulposus (NP), the central, gelatinous region of the IVD, have been the subject of much work (Di Martino et al., 2005; Hegewald et al., 2008; Sebastine and Williams, 2007). The limited success that has been achieved by these methods, however, stems in part from the fact that the annulus fibrosus (AF), the outer ring of the IVD, is not repaired. The AF is necessarily damaged during surgery to remove or repair the NP, and yet a functional, intact AF is key to preventing re-herniation of the NP and retention of any NP replacement device (Alini et al., 2002; Wilke et al., 2006). Thus, the ultimate success of such a treatment depends in part on the restoration of AF function.
Methods for repairing damaged AF are currently limited largely to sutures and modified sutures, which do not compensate for the loss of AF tissue or restore the lost biomechanical properties (Bron et al., 2009a). An appealing alternative is the development of a tissue engineering scaffold to repair the gap in the AF and contain the NP or its replacement. Such a scaffold would need to meet the following three requirements: match the mechanical properties of the AF tissue, support the growth of disc cells, and adhere to the surrounding tissues under physiological levels of strain. A number of materials have been investigated for this purpose including gels, bioglass, collagen, silk and degradable polymers such as polycaprolactone and polyglycolic acid. (Chang et al., 2007; Helen and Gough, 2008; Mizuno et al., 2004; Nerurkar et al., 2007; Sato et al., 2003; Shao and Hunter, 2007; Wan et al., 2008). While many of these materials show promise, none have satisfactorily addressed the need for fixing the scaffold within the annular defects. To ensure a scaffold remains in place and encourage the formation of new tissue, it is critical that any material be able to strongly adhere and be fully integrated with the native annulus tissue.